feat: add email-html-pro plugin with HTML email and raw HTML support

[abesticode]

Plugin Submission Form

1. Metadata

• Plugin Author: abesticode
• Plugin Name: email_html_pro
• Repository URL: https://github.com/abesticode/dify-plugin-email-html-pro

2. Submission Type

• New plugin submission
• Version update for existing plugin

3. Description

This PR introduces the email-html-pro plugin, an enhanced email sending tool for Dify workflows with advanced HTML support.

Key Features:

• HTML Email Support: Send beautifully formatted HTML emails with full styling support
• Raw HTML Mode: Bypass markdown-to-HTML conversion to send custom HTML templates exactly as designed
• Attachment Support: Include file attachments in your emails
• Batch Email Sending: Send emails to multiple recipients efficiently
• SMTP Configuration: Works with any SMTP provider (Gmail, AWS SES, SendGrid, etc.)

Tools Included:

1. send_mail - Send a single email with HTML content and optional attachments
2. send_mail_batch - Send batch emails to multiple recipients

Use Cases:

• Marketing emails with rich HTML templates
• Transactional emails from Dify workflows
• Notification emails with custom branding
• Automated report delivery with attachments

4. Checklist

• I have read and followed the Publish to Dify Marketplace guidelines
• I have read and comply with the Plugin Developer Agreement
• I confirm my plugin works properly on both Dify Community Edition and Cloud Version
• I confirm my plugin has been thoroughly tested for completeness and functionality
• My plugin brings new value to Dify

5. Documentation Checklist

• Step-by-step setup instructions
• Detailed usage instructions
• All required APIs and credentials are clearly listed
• Connection requirements and configuration details
• Link to the repository for the plugin source code

6. Privacy Protection Information

Data Collection

This plugin processes email addresses and email content provided by the user during workflow execution. No personal data is stored or collected by the plugin itself. All data is transmitted directly to the configured SMTP server.

Privacy Policy

• I confirm that I have prepared and included a privacy policy in my plugin package based on the Plugin Privacy Protection Guidelines